Hydrodealkylation process with promoted group viii metals

ABSTRACT

A hydrodealkylation process comprising contacting alkyl aromatic hydrocarbons with a catalyst, including an active Group VIII metal, such as, platinum, rhodium, palladium, ruthenium and nickel, a promoter selected from the group of alkali, alkaline earth and rare earth metals, such as, potassium, rubidium, cesium, calcium, strontium, cerium and thorium, and an inert oxide support such as, gamma aluminas, silica-alumina, silica, silica-magnesia, alumina-magnesia and silica-zirconia at a temperature of 1,050* to 1,200* F, a pressure of 100 to 1,000 psig., a liquid hourly space velocity of 0.1 to 5 and a hydrogento-hydrocarbon mole ratio of 3-15/1.

United States Patent Kovach et a1.

[ Oct. 24, 1972 [54] HYDRODEALKYLATION PROCESS WITH PROMOTED GROUP VIIIMETALS [72] Inventors: Stephen M. Kovach, Ashland; Ralph E. Patrick,Flatwoods; Ronald A.

[21] Appl. N0.: 769,729

[52] U.S. Cl ..260/672 R, 208/110, 208/112,

[51] Int. Cl ..B0lj 11/06, C07c 3/58 [58] Field of Search ..260/672 [56]References Cited UNITED STATES PATENTS 2,861,959 11/1958 Thorn et a1...252/465 2,814,599 11/ 1957 Lefrancois et a1. ..252/466 2,780,5802/1957 Doumani ..208/137 2,894,898 7/ 1959 Oettinger et a1 ..208/1122,976,232 3/1961 Porter et a1 ..208/138 3,436,433 4/1969 Lester..260/672 3,436,434 4/1969 Lester ..260/672 2,422,673 6/ 1947 Haensel eta1. ..260/672 2,734,929 2/ 1956 Doumani ..260/672 2,858,348 10/ 1958Bosmajian et a1. ..260/668 3,193,592 7/ 1965 Eubank ..260/672 3,222,41012/ 1965 Swanson ..260/672 3,236,904 2/ 1966 Pickert ..260/672 3,306,944 2/1967 Pollitzer ..260/ 672 3,478,120 11/ 1969 Myers et a1..260/672 2,780,584 2/1957 Doumani ..208/137 Primary ExaminerDelbert E.Gantz Assistant Examiner-G. E. Schmitkons Attorney-Walter H. Schneider IABSTRACT A hydrodealkylation process comprising contacting alkylaromatic hydrocarbons with a catalyst, including an active Group VIIImetal, such as, platinum, rhodium, palladium, ruthenium and nickel, apromoter selected from the group of alkali, alkaline earth and rareearth metals, such as, potassium, rubidium, cesium, calcium, strontium,cerium and thorium, and an inert oxide support such as, gamma aluminas,silicaalumina, silica, silica-magnesia, alumina-magnesia andsilica-zirconia at a temperature of 1,050 to 1,200 F, a pressure of 100to 1,000 psig., a liquid hourly space velocity of 0.1 to 5 and ahydrogen-to-hydrocarbon mole ratio of 3-1 5/ 1.

4 Claims, No Drawings BACKGROUND OF THE INVENTION The present inventionrelates to a process for the hydrodealkylation of alkyl aromatics to theparent aromatic hydrocarbons. More specifically, the present inventionrelates to a process for the hydrodealkylation of alkyl aromatichydrocarbons to the parent aromatic hydrocarbons, utilizing a uniquecatalyst system.

The hydrodealkylation of alkyl aromatics has been practiced for manyyears. The principal processes involve the conversion of toluene andlike alkyl-substituted benzenes to benzene, and coal tar light oils andcoal tar methyl naphthalene to benzene and naphthalene, respectively.These processes may be catalytic or non-catalytic in nature. Thenon-catalytic system which involves thermal dealkylation, in thepresence of hydrogen, requires high temperatures and pressures. Whilethe catalytic processes require lower temperatures and pressures, thesetemperatures and pressures are still quite high and therefore result inshort catalyst life. Most commercial catalytic processes employchromia-magnesia deposited on an alumina base as a catalyst. Since thedevelopment of this catalyst, there has really been no improvement incatalysts for this reaction.

It is therefore an object of the present invention to provide a newprocess for the hydrodealkylation of alkyl aromatics employing a novelcatalyst system. In a more specific aspect, the present inventionrelates to the process for the hydrodealkylation of alkyl aromaticswherein catalysts which improve conversion are employed. Another andfurther object of the present invention is to provide a process for thehydrodealkylation of aromatics wherein catalysts of higher selectivityare utilized. A still further object of the present invention is toprovide an improved process for the hydrodealkylation of alkyl aromaticswherein catalysts which reduce carbon lay-down on the catalyst areemployed. A further object of the present invention is to provide animproved hydrodealkylation process for the hydrodealkylation of alkylaromatics wherein novel catalysts are employed which permit operation atlower than conventional temperatures. Another and further object of thepresent invention is to provide an improved system for thehydrodealkylation of alkyl aromatics wherein catalysts are employedwhich permit the use of lower hydrogen partial pressures.

SUMMARY OF THE INVENTION DESCRIPTION OF THE PREFERRED EMBODIMENTSSuitable feedstocks for use in accordance with the present inventioninclude toluene, polymethyl benzenes, coal tar light oils, coal tarmethylnaphthalene concentrates, and bicyclic concentrates from lightcycle oils and heavy reformates. Feedstock preparation includesfractionation to remove front ends or bottoms to thereby removeundesired fractions such as unsaturates, indanes and resinous materials.For example, it has been found that coal tar methylnaphthaleneconcentrates, as received from the coke oven, contain a large amount ofcontaminants, such as polymers, resins and free carbon. Distillation ofsuch raw materials to yield a percent overhead leaves these materials asa bottoms. Hydrogenation and hydrotreating of the overhead fractionremoves sulfur, nitrogen and oxygen contaminants, but, due to thethermal instability of the 'feedstocks, a heavy resinous material isproduced through thermal polymerization. Distillation of thehydrotreated product is required to remove these resins andftherebyreduce carbon laydown on the hydrodealkylation catalyst and reducehydrogen consumption due to hydrocracking of the resins and polymers.

The processing conditions for the hydrodealkylation reaction of thepresent invention include a temperature between about 1,050 and 1,200"F, a pressure between about and 1,000 psig., a liquid hourly spacevelocity between about 0.1 and 5, and a hydrogen-tohydrocarbon moleratio of about 3 to 15/ 1.

The catalysts to be employed in accordance with the present inventioninclude metal oxides from Group VHI of the Periodic System, particularlyplatinum, rhodium, palladium, ruthenium and nickel. The promotersinclude alkali metal oxides of Group I of the Periodic System, alkalineearth metal oxides of Group II of the Periodic System and the rare earthmetals. Examples of materials of this nature which may be employedinclude potassium, rubidium and cesium; calcium and strontium, andcerium and thorium, etc. The active metal and the promoter are depositedon an inert oxide support, which preferably includes a high area aluminahaving a boehmite, bayerite, beta, or eta crystalline form, or otheraluminas, silica-alumina, silica, silica-magnesia, silica-zirconia,alumina-magnesia, etc.

The optimum active metal content of the catalyst is about 0.5 to 5percent by weight based on the final catalyst. The metal oxide promotershould be present in amounts of about 1 to 10 percent by weight.

The catalysts of the present invention may be prepared by well-knownimpregnation techniques. One may employ extrudates or pellets forimpregnation or powders followed by pelletization or extrusion to yieldthe finished catalyst. The active metal and the promoter may be addedthrough the use of water-soluble salts, such as their halides, nitrates,sulfates, acetates, etc. Easily hydrolyzed salts can be kept in solutionwithout decomposition by employing appropriate inorganic acids.

The following examples illustrate methods of preparing the compositecatalysts of the present invention.

EXAMPLE I To ml. of distilled water was added 2 g. of rhodiumtrichloride. This solution was added to 150 ml. of boehrnite aluminapellets and after contact for fifteen minutes the unadsorbed liquid wasdecanted from the catalyst pellets. The resulting impregnated catalystwas dried at 250 F for 1 hour and calcined at 950 F in air in a mufflefurnace for 16 hours. This yielded a catalyst of the followingcomposition:

1% Rh4% K O-Al O EXAMPLE II By employing the techniques and procedureoutlined in Example 1, other catalysts were prepared. A solutioncontaining cesium nitrate was added to a boehmite alumina. Drying andcalcination of this impregnated catalyst yielded the followingcomposition:

An aqueous solution of chloroplatinic acid added to pellets of 4% Cs OA1O followed by drying and calcination yielded a catalyst of the followingcomposition:

USE OF CATALYSTS FOR HYDRODEALKYLATION In order to illustrate theeffectiveness of the catalysts of the present invention and the processfor hydrodealkylation, a toluene feed was subjected to a temperature of1,150 F, a pressure of 500 psig., a liquid hourly space velocity of 0.5,and a hydrogen-to-hydrocarbon mole ratio of 5:1, utilizing a commercialcatalyst of chromia-magnesia on alumina as compared with certain of thecatalysts of the present invention. The results of these Runs are shownin Table I. In a similar comparative run under exactly the sameconditions, a topped, commercial, coal tar methyl naphthalene cut at 500F and having the composition set forth in Table II was utilized with theresults shown in Table Il.

Catalyst 12Cr-2Mg-A1,0, 1 RhtCs-ALO; Product Distribution Naphthalene37.8 41.0 Naphthalene 59.0 53.8 Methylnaphthalene 1.4 0.5Dimethylnaphthalene 2.9 4.7 Wt. Feed Me Naphthalene Conversion 97 Carbonon Catalyst Wt. Feed 1.32 0.82 Wt.

Naphthalene 50.4 Naphthalene 30.4 Methylnaphthalene 13.4Dimethylnaphthalene 5.8

The catalysts of the present invention may be utilized with sulfur ornone-sulfur containing feedstocks. Preferably, however, a feedstockcontaining small amounts of sulfur, for example 10 to 100 ppm, willminimize hydrocracking activity without impairing the hydrodealkylationactivity of the catalyst.

The process of the present invention is further illustrated by thefollowing examples in which a Group VIII metal was combined with analkaline earth metal and with a rare earth metal and used as a catalystfor the process.

TABLE III Hydrodealkylation of Toluene Conditions: 1 F, 500 PSIG, 0.5

LHSV, 5/1 H,H'C Feed: Toluene Wt. Feed When reference is made herein tothe Periodic System of elements, the particular groupings referred toare as set forth in the Periodic Chart of the Elements, in The MerckIndex, Seventh Edition, Merck & Co., Inc., 1960.

What is claimed is:

l. A process wherein hydrodealkylating dealkylatable hydrocarbonmaterials is the dominant reaction, comprising: contacting thehydrocarbon materials with a catalyst consisting essentially of about0.5 to 5 percent by weight of an active metal selected from the Groupconsisting of platinum, rhodium, palladium, ruthenium, and nickel andabout 1 to 10 percent by weight of a promoting metal selected from thegroup consisting of cerium, thorium and mixtures thereof, bothimpregnated on an inert oxide carrier selected from the group consistingof alumina, silica, magnesia, zirconia, and mixtures thereof underconditions sufiicient to effect said hydrodealkylation reaction,including a temperature of about 1,050 to 1,200 F, a pressure of about100 to 1,000 psig, a liquid hourly'space velocity of about 0.1 to 5 anda gaseous hydrogen to inlet feed hydrocarbon mole ratio between about 3and 15 to 1.

2. A process wherein hydrodealkylating dealkylatable methyl-substitutedaromatic hydrocarbons is the dominant reaction comprising: contactingthe hydrocarbons with a catalyst consisting essentially of about 0.5 to5 percent by weight of an active metal selected from the groupconsisting of platinum, rhodium, palladium, ruthenium, and nickel andabout 1 to percent by weight of a promoting metal selected from thegroup consisting of cerium, thorium, and mixtures thereof, bothimpregnated on an inert oxide carrier selected from the group consistingof alumina, silica, magnesia, zirconia, and mixtures thereof underconditions sufficient to efiect said hydrodealkylation reaction,including a temperature of about 1,050 to l,200 F, a pressure of about100 to 1,000 psig, a liquid hourly space velocity of about 0.1 to 5, anda gaseous hydrogen to inlet feed hydrocarbon mole ratio between about3and 15 to 1.

3. A process in accordance with claim 1 wherein the inert oxide carrieris a gamma alumina.

4. A process in accordance with claim 1 wherein the promoting metal isin its oxide form.

2. A process wherein hydrodealkylating dealkylatable methyl-substitutedaromatic hydrocarbons is the dominant reaction comprising: contactingthe hydrocarbons with a catalyst consisting essentially of about 0.5 to5 percent by weight of an active metal selected from the groupconsisting of platinum, rhodium, palladium, ruthenium, and nickel andabout 1 to 10 percent by weight of a promoting metal selected from thegroup consisting of cerium, thorium, and mixtures thereof, bothimpregnated on an inert oxide carrier selected from the group consistingof alumina, silica, magnesia, zirconia, and mixtures thereof underconditions sufficient to effect said hydrodealkylation reaction,including a temperature of about 1, 050* to 1,200* F, a pressure ofabout 100 to 1,000 psig, a liquid hourly space velocity of about 0.1 to5, and a gaseous hydrogen to inlet feed hydrocarbon mole ratio betweenabout 3 and 15 to
 1. 3. A process in accordance with claim 1 wherein theinert oxide carrier is a gamma alumina.
 4. A process in accordance withclaim 1 wherein the promoting metal is in its oxide form.